System and method for dynamic control of a heat exchanger

ABSTRACT

The present application relates to a system for dynamic control of the operation of a heat exchanger, the system comprising a heat exchanger, a plurality of injector arrangements, a local sensor arrangement, and a controller, wherein the local sensor arrangement comprises a plurality of local temperature sensors being arranged to measure temperature values; and wherein the controller is arranged to determine a difference between the measured temperature values and is further arranged to communicate with the valves of the plurality of injector arrangements to adjust the local amount of first fluid supplied by at least one of the injector arrangements in order to even out the determined difference. The application also relates to a method for the dynamic control of the operation of a heat exchanger in such a system.

TECHNICAL FIELD

The present invention refers generally to a system for dynamic controlof the operation of a heat exchanger. Further, the invention refers to amethod for dynamic control of the operation of a heat exchanger.

BACKGROUND ART

The present invention refers generally to a system comprising a heatexchanger and in particular to a heat exchanger in the form of a plateheat exchanger. Different types of heat exchangers are based ondifferent techniques. One type of heat exchanger utilizes evaporation ofa fluid, such as a cooling agent, for various applications, such as airconditioning, cooling systems, heat pump systems, etc. Thus, the heatexchanger may be used in a two-phase system handling a fluid in a liquidform as well as in an evaporated form.

In case of the evaporator being a plate heat exchanger, this may includea plate package, which comprises a number of first and second heatexchanger plates. The plates are permanently joined to each other andarranged side by side in such a way that a first plate interspace,forming a first fluid passage, is formed between each pair of adjacentfirst heat exchanger plates and second heat exchanger plates, and asecond plate interspace, forming a second fluid passage, between eachpair of adjacent second heat exchanger plates and first heat exchangerplates. The first plate interspaces and the second plate interspaces areseparated from each other and provided side by side in an alternatingorder in the plate package. Substantially each heat exchanger plate hasat least a first porthole and a second porthole, wherein the firstportholes form a first inlet channel to the first plate interspaces andthe second portholes form a first outlet channel from the first plateinterspaces. The plate package includes a separate space for each ofsaid first plate interspaces, which space is closed to the second plateinterspaces.

In this general prior art plate heat exchanger, to be used in atwo-phase system, a first fluid, such as a cooling agent, is introducedinto a valve in liquid form but expands when going through the valve,due to the pressure drop, into a partly evaporated fluid at one end ofthe first inlet channel, i.e. the first port hole, for furtherdistribution along the first inlet channel and further into each of theindividual first plate interspaces during evaporation into an evaporatedform. There is always a risk that the energy content of the suppliedfluid is too high, whereby a part of the flow supplied to the inletchannel via its inlet port will meet the rear end of the inlet channeland be reflected thereby in the opposite direction. Thereby the flow inthe inlet channel is very chaotic and hard to predict and control.

Further, the pressure drop of the cooling agent may increase with thedistance from the inlet to the first inlet channel, whereby thedistribution of the first fluid between the individual plate interspaceswill be affected.

It is also known that the angular flow change, which the droplets of thefirst fluid must undergo when entering the individual plate interspacesfrom the first inlet channel, contributes to an uneven distribution.

Yet another influencing parameter is dimensional differences between theindividual first plate interspaces, resulting in that each first plateinterspace has its unique efficiency.

It is also known that the operation and performance of an individualfirst plate interspace depends on its position in a plate package. Theoutermost first plate interspaces on each side of the plate package tendto behave differently than those in the middle of the plate package.

As a result of this it is very hard, if not impossible, to optimize theoperation and efficiency of an heat exchanger as a whole, ensuring thatall fluid supplied to the evaporator of the heat exchanger is fullyevaporated before leaving the outlet of the evaporator and especiallybefore reaching the inlet of a compressor to be arranged downstream ofthe outlet of the evaporator, and also ensuring that the heat exchangerfunctions with high efficiency and capacity during different workingconditions. In fact, it is sufficient that there is one malfunctioningfirst plate interspace for insufficient evaporation of the evaporator asa whole to occur. For example, if a single first plate interspace isflooded, i.e. is incapable of evaporating the complete amount of fluidsupplied thereto, droplets will occur downstream the outlet of theevaporator. Generally, by fully evaporated means that the evaporatedfluid must have reached superheated state whereby the evaporated fluidcomprises dry evaporated fluid only, i.e. the evaporated fluid shouldhave a temperature being higher than the saturation temperature at aprevailing pressure.

The superheating, being a physical parameter well known in the art, isdefined as the temperature difference between the present temperatureand the saturation temperature at a prevailing pressure, i.e. when thereis not any liquid content remaining in the fluid. The superheating isunique for a given fluid and for a given temperature and pressure. Thesaturation temperature may be found in conventional graphs or tables.

The purpose of operating the evaporator of the heat exchanger as closeto a set-point superheating value as possible no matter operation dutyis of importance to get as high utilization factor as possible. Thus, itis of economic importance. Further, it has an influence to othercomponents cooperating with the evaporator, such as a compressor, sincecompressors normally are sensitive to liquid content. Any dropletsremaining in the evaporated fluid when reaching the inlet of thecompressor may damage the same. Also, there is an economical interest ofoperating the evaporator with a superheating being as low as possiblesince once the fluid has reached the superheated state the fluid iscompletely dry and there is no substantial gain in increasing thetemperature additionally.

The set-point superheating above is determined by the systemmanufacturer to incorporate a certain wanted safety margin against therisk of receiving liquid into the compressor. The problems discussedabove get more pronounced when the load of the evaporator is changed.For example, this may be the case when changing the operation duty of anair conditioning system, from one temperature to another, meaning thatthe amount of fluid to be supplied to the evaporator is changed.

Documents EP2156112B1 and WO2008151639A1 disclose a method forcontrolling a refrigerant distribution among at least two evaporators insuch a manner that the refrigeration capacity of air-heated evaporatorsis utilized to the greatest possible extent. This is made by monitoringa superheat of refrigerant at a common outlet of the evaporators.Further, this is made by altering a mass flow of refrigerant through aselected evaporator while keeping the total mass flow of refrigerantthrough all the evaporators substantially constant. The flow iscontrolled by one single valve being an expansion valve. Thus, the twodocuments provide a solution to controlling the operation of a pluralityof air-heated evaporators, in which method each evaporator is evaluatedas a complete unit and in which method each unit is controlled in viewof additional evaporators arranged in the same circuit.

Generally, the efficiency of heat exchangers, and especially plate heatexchangers, at part load is a raising issue. More focus is put on howthe evaporator of the heat exchanger performs at different operationduties instead of being measured at only one operation duty. Forexample, laboratory scale trials have shown that an air-conditioningsystem can save 4-10% of its energy consumption just by improvedevaporator function at part load for a given brazed plate heatexchanger. Further, a heat exchanger system is typically only operatingat full capacity for 3% of the time, while most heat exchangers aredesigned and tuned for a full capacity operation.

SUMMARY

The object of the present invention is to provide an improved heatexchanger system remedying the problems mentioned above. Especially itis aimed at a heat exchanger system and a method which allows a bettercontrol of the supply of the first fluid, such as the cooling agent,between the fluid passages to thereby improve the efficiency of theplate heat exchanger no matter running condition.

This object is achieved by a system for dynamic control of the operationof a heat exchanger, the system comprising a heat exchanger, a pluralityof injector arrangements, a local sensor arrangement, and a controller,wherein the heat exchanger comprises a first global outlet, a firstplurality of fluid passages, each fluid passage comprising a local inletand a local outlet, for the supply of a first fluid to the first globaloutlet via the first plurality of fluid passages during evaporation ofthe first fluid, the heat exchanger further comprises a second globaloutlet, a second plurality of fluid passages, each fluid passagecomprising a local inlet and a local outlet, for the supply of a secondfluid to the second global outlet via the second plurality of fluidpassages, the first fluid passages and the second fluid passages arearranged separated from each other and side-by-side, in order to enableheat exchange between the first fluid in the first plurality of fluidpassages and the second fluid in the second plurality of fluid passages,each injector arrangement comprises at least one valve, and eachinjector arrangement is arranged to supply a flow of the first fluid tothe local inlet of at least one of the first plurality of fluidpassages, the local sensor arrangement comprises a plurality of localtemperature sensors being arranged to measure temperature valuescorresponding to the local temperature of the evaporated first fluidflowing nearby the local outlets of the first plurality of fluidpassages, the controller is arranged to determine a difference betweenthe measured temperature values received from the local sensorarrangement and is further arranged to communicate with the valves ofthe plurality of injector arrangements to adjust the local amount offirst fluid supplied by at least one of the injector arrangements inorder to even out the determined difference.

The local adjustment is performed in order to even out any temperaturedifferences in view of the first fluid flowing nearby the local outlets.The overall ambition with the local adjustment may thus be seen as theambition that all first fluid passages should contribute equally to theoverall operation of the evaporator. This is achieved by the inventivesystem in which the operation of each fluid passage or a subset of fluidpassages may be monitored, whereby the contribution from each individualfluid passage to the overall performance of the heat exchanger may beadjusted.

For example, in known heat exchangers, the global amount of flow isadjusted if liquid content is detected in the global outlet ordownstream from the global outlet. However, the presence of liquidcontent in the global flow may be caused by a local overflow in a singlefluid passage or in a subset of fluid passages. By measuring localtemperatures and evening out the differences between the temperatures inthe first fluid flowing nearby the local outlets, only the local flow inthe specific fluid passage or passages causing the liquid content isadjusted.

By the inventive system and method, the first plurality of fluidpassages may be utilized more efficiently as compared to knowntechniques. Further, by optimizing the flow in the plurality of firstfluid passages, a higher pressure may be achieved in the global flowdownstream from the global outlet. In some systems, the efficiency ofthe compressor is increased when fed with a higher pressure. Thus, theefficiency of the whole system may be boosted.

The plurality of local temperature sensors in the local sensorarrangement may be arranged nearby the local outlets of the firstplurality of fluid passages.

Alternatively, the plurality of local temperature sensors in the localsensor arrangement may be arranged nearby the local outlets of thesecond plurality of fluid passages.

By the term nearby is meant around the local outlet, i.e. it could beboth upstream and downstream from the local outlet in view of the firstfluid. The local temperature sensors should be positioned such that theymeasure on flows of first fluid after the flows have evaporated andbefore the flows mix with each other to form a global flow.

The local temperature sensors may be arranged in through holes having anextension from the exterior of a plate package of the heat exchanger tothe interior. Alternatively, the local temperature sensors may bearranged only interior or only exterior of the plate package.

The local temperature sensors may be arranged to measure temperatures inconnection to one or more fluid passages. Alternatively, the localsensor sensors may be arranged to measure an average temperature value.

It is to be understood that by measuring temperature valuescorresponding to the local temperature of the evaporated fluid is meantthat the measurement does not need to be performed directly on or indirect connection to the first fluid flowing nearby the local outlets.

The controller may be further arranged to determine a compensating localadjustment of the local amount of first fluid supplied by the other thanthe at least one of the injector arrangements such that the globalamount of first fluid in the plurality of first passages remains thesame. The controller may be further arranged to communicate thedetermined compensating local adjustment to said other than the at leastone of the injector arrangements.

The compensating local adjustment is determined in order to keep theglobal amount of first fluid in the plurality of first passagesunaffected by the local adjustments. The global amount may instead becontrolled based on values measured by a global sensor arrangement.

The controller may be arranged to determine the difference by at leastdetermining the standard deviation for the measured temperature values.By utilizing the standard deviation for determining the localadjustment, quick and harsh local adjustments are damped such that theadjustment procedure becomes more smooth and even.

It is to be understood that the difference may be determined in manyways and based on the exact measured temperature values or amodification, such as a mean value or adjustment, of one or moremeasured temperature values. Moreover, one or more differences may bedetermined based on a single batch of measured temperature values.

The first fluid may be a refrigerant. The second fluid may comprisewater. The second fluid may be brine or may consist of only water.

The system may be adapted such that different types of first fluids maybe supplied through the system. For example, the system may comprisedifferent sections of fluid passages for the supply of different firstfluids.

The controller may be a P regulator, a PI regulator or a PID regulator.These regulator types are well known in the field of automatic controlengineering. The PID regulator may be used to relatively fast processand react on values, such as measured temperature and/or pressurevalues, without causing any self-oscillation of the system.

It is appreciated that other types of conventional controllers may befeasible as well.

The system may further comprise a global sensor arrangement beingarranged to measure the global temperature and the global pressure, orthe presence of any liquid content, of the evaporated first fluiddownstream from the first global outlet. Further, the controller may bearranged to communicate with the valves of the plurality of injectorarrangements, or with a global valve, to control, based on informationreceived from the global sensor arrangement, the global amount of thefirst fluid to be supplied to the first plurality of fluid passages inorder for the heat exchanger to operate towards a set-point superheatingvalue.

The term “liquid content” is in the context of this application definedas fluid being in a liquid phase or a mixed liquid/gaseous phase. It mayfor example be in the form of droplets.

The purpose of the global sensor arrangement is to determine thepresence of any liquid content in the evaporated first fluid, or todetermine the so called superheating of the evaporated first fluid. Themeasurements are transmitted to the controller which, in turn,determines a global adjustment of the flow of first fluid in the firstplurality of fluid passages.

Thus, the local flow in a subset of the first plurality of fluidpassages may be controlled by measuring local temperature values by thelocal sensor arrangement, and the global flow in the first plurality offluid passages may be controlled by measuring global temperature and/orpressure values by the global sensor arrangement.

The global adjustment may be described as an adjustment in order tooperate towards a set-point superheating or towards the non-presence ofliquid content, whereas the local adjustment may be described as anadjustment for evening out the temperature differences within the heatexchanger. Both adjustments are performed in order to optimize theperformance of the heat exchanger. The adjustments complement each otherbut may also function alone. For example, a system may comprise thelocal sensor arrangement and perform the local tuning of the firstplurality of fluid passages without utilizing the global sensorarrangement and global adjustment. Furthermore, the global adjustmentmay be performed by another arrangement than the global sensorarrangement.

The two processes of local adjustment and global adjustment arepreferably performed continuously for the system during operationthereof. Thus, the local flow and the global flow are adjustedcontinuously whereby the heat exchanger is continuously optimized inview of current running conditions and operation duty. The heatexchanger thus becomes more flexible and adapts to different runningconditions. The heat exchanger will run in an optimized mannerregardless of the running conditions.

The two processes may be performed as parallel loops in the controller.

The global sensor arrangement may comprise a global temperature sensorand a global pressure sensor. Based on a measured global temperaturevalue and a measured global pressure value, the superheating may bedetermined by the controller. The two global sensors must not have thesame position within the system. However, it may be preferred that theglobal sensor arrangement is arranged at essentially the same position,such that the global sensors measures on the same portion of evaporatedfirst fluid.

Provided the global sensor arrangement is arranged to measure globaltemperature and global pressure, the set-point superheating value mayfor example be the superheating for the specific fluid used as firstfluid in the system.

Alternatively, the superheating value may be the calculated superheatingfor the specific fluid used in the system as adjusted with apre-determined safety margin. In case the global sensor arrangement isarranged to instead measure the presence of any liquid content in theevaporator, the set-point superheating value may be handled in a“digital” manner, wherein presence of any liquid content is an indicatorof the amount of fluid supplied to the evaluated fluid passage being toohigh for a complete evaporation, or alternatively, no presence of anyliquid content is an indicator of the amount of fluid supplied to thefluid passage being insufficient and may be increased.

Alternatively, in case the global sensor arrangement is arranged tomeasure the presence of any liquid content in the evaporated fluid, theglobal sensor arrangement may be at least one global temperature sensor.The global temperature sensor may be used for determining a tendency ofdecreasing global temperature as seen over a measuring period or be usedfor determining an unstable global temperature as seen over a measuringperiod. Both a tendency of decreasing global temperature and an unstableglobal temperature may be used as input to the controller to establishthe presence of any liquid content in the evaporated fluid since theliquid content, i.e. a fluid flow being in liquid phase or in a mixedliquid/gaseous phase will indicate a lower temperature on the globaltemperature sensor than a fully evaporated, dry gaseous fluid flow. Thisprinciple is also applicable to the local temperature sensors, i.e. thelocal temperature sensors may be utilized to detect the presence of anyliquid content in one or a subset of fluid passages in the firstplurality of fluid passages. Thus, the local sensor arrangement may insome embodiments function on its own without the global sensorarrangement.

According to another aspect, the invention relates to the use of asystem according to any of the above disclosed embodiments of thesystem.

According to another aspect, the invention relates to a method fordynamic control of the operation of a heat exchanger in a systemaccording to any of the above disclosed embodiments, the methodcomprising the steps of:

a) supplying, by the plurality of injector arrangements, a first fluidto the local inlets of the first plurality of fluid passages, andsupplying a second fluid to the local inlets of the second plurality offluid passages;

b) measuring, by the local sensor arrangement, temperature valuescorresponding to the local temperatures of the evaporated fluid flowingnearby the local outlets of the first plurality of fluid passages;

c) transmitting the measured temperature values to the controller;

d) determining, by the controller, a difference between the measuredtemperature values;

e) determining, by the controller, a local adjustment of the localamount of fluid supplied by at least one of the plurality of injectorarrangements based on the determined difference, in order to even outthe determined difference,

f) communicating, by the controller, with the valves of the plurality ofinjector arrangements to adjust the local amount of first fluid suppliedby at least one of the plurality of injector arrangements according tothe determined local adjustment.

The method may further comprise the step of determining a compensatinglocal adjustment of the local amount of first fluid supplied by theother than the at least one of the injector arrangements in order tokeep the global amount of first fluid in the plurality of first passagesunaffected by the local adjustments. The method may further comprise thestep of communicating, by the controller, with the valves of theplurality of injector arrangements to adjust the local amount of firstfluid supplied by said other than the at least one of the plurality ofinjector arrangements according to the determined compensating localadjustment.

The step of determining the difference may comprise determining thestandard deviation for the measured temperature values.

The method may be performed in a system further comprises a globalsensor arrangement comprising a global temperature sensor and a globalpressure sensor, wherein the method further comprising the steps of:

g) measuring, by the global sensor arrangement, a global temperaturevalue and a global pressure value of the evaporated first fluiddownstream from the first global outlet;

h) transmitting the measured global temperature value and measuredglobal pressure value to the controller;

i) determining, by the controller, the superheating value based on themeasured global temperature value and the measured global pressurevalue;

j) determining, by the controller, the difference between the determinedsuperheating value and a set-point superheating value, or the presenceof any liquid content in the evaporated first fluid;

k) determining, by the controller, a global adjustment of the amount offirst fluid supplied by the plurality of injector arrangements, requiredto reach the set-point superheating value,

l) communicating, by the controller, with the valves of the plurality ofinjector arrangements, or with a global valve, to adjust the globalamount of first fluid supplied by the plurality of injector arrangementsaccording to the determined global adjustment.

The steps b)-f) and the steps g)-l) may be performed in parallel.

The steps b)-f) and the steps g)-l) may be continuously performed. Thesteps b)-f) and the steps g)-l) may be performed as parallel loops inthe controller.

The disclosed features and advantages disclosed in connection to thesystem are relevant for this aspect relating to the method as well. Inorder to avoid undue repetition, reference is made to the above aspectrelating to the system.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, for example, withreference to the accompanying schematic drawings, in which

FIG. 1 schematically illustrates a prior art refrigeration circuit beinga mechanical vapor compression system.

FIG. 2 schematically illustrates a side view of a typical plate heatexchanger.

FIG. 3 schematically illustrates a front view of the plate heatexchanger of FIG. 2.

FIG. 4 schematically illustrates a cross section along an edge of aprior art plate heat exchanger.

FIG. 5 illustrates a refrigeration circuit relating to the inventivesystem.

FIG. 6 illustrates injector arrangements for providing a fluid into thefirst plurality of fluid passages.

FIGS. 7-9 illustrate the positioning of the local sensor arrangement indifferent embodiments of the present invention.

FIG. 10 illustrates a method for controlling the local flow in the heatexchanger according to one embodiment of the present invention.

FIG. 11 illustrates a method for controlling the global flow in a heatexchanger.

DETAILED DESCRIPTION

A heat exchanger 1 may typically be included as an evaporator in arefrigeration circuit. A prior art refrigeration system, see FIG. 1,being a mechanical vapor compression system, typically comprises acompressor 51, a condenser 52, an expansion valve 53 and an evaporator54. The circuit may further comprise a pressure sensor 55 and atemperature sensor 56 arranged between the outlet of the evaporator andthe inlet of the compressor. The refrigeration circle of such systemstarts when a cooling agent enters the compressor 51 in evaporated formwith a low pressure and with a low temperature. The cooling agent iscompressed by the compressor 51 to a high pressure and high temperatureevaporated state before entering the condenser 52. The condenser 52precipitates the high pressure and high temperature gas to a hightemperature and high pressure liquid by transferring heat to a lowertemperature medium, such as water or air. The high temperature liquidthen enters the expansion valve 53 where the expansion valve allows thecooling agent to enter the evaporator 54.

The expansion valve 53 has the function of expanding the cooling agentfrom the high to the low pressure side, and to fine tuning the flow. Inorder for the higher temperature to cool, the flow into the evaporatormust be limited to keep the pressure low and allow evaporation back intothe evaporated form. The expansion valve 53 may be operated by acontroller 57 based on signals received from the pressure sensor 55 andthe temperature sensor 56. The information may be used to indicate theoverall operation of the evaporator 54 based on a so called superheatingbeing indicative of any liquid content remaining in the fluid afterleaving the evaporator 54.

Now turning to FIGS. 2 to 4 in which an evaporator in the form of aplate heat exchanger 1 is illustrated. It is to be understood that theheat exchanger 1 may be of any type, such as a plate heat exchanger, apipe and shell heat exchanger, a spiral heat exchanger etc. Theinvention will however in the following be discussed as applied to aplate heat exchanger 1, although the invention is not to be limitedthereto.

Throughout the application, the terms local and global will be used. Theterm local, as used in local amount of flow, a local temperature, localinlets and local outlets, refers to a subset of the total system. Forexample, a local amount of flow in the first plurality of fluid passagesrefers to an amount of flow in a subset of the first plurality of fluidpassages, such as one fluid passage in the first plurality of fluidpassages. Another example is that each fluid passage has a local inletand a local outlet. Yet another example is that local temperature of thefirst fluid refers to a temperature at a certain position in the firstfluid, such as the temperature of the first fluid flowing in one fluidpassage in the first plurality of fluid passages.

On the contrary, the term global refers to the total system. Forexample, the global amount of flow of the first fluid in the firstplurality of fluid passages refers to the total amount of flow of thefirst fluid in the evaporator. Thus, by adjusting the global amount offlow, all injector arrangements are adjusted, by increasing ordecreasing the flow, to an equal amount. Another example is that theheat exchanger has a global outlet, meaning the outlet where the localflows from subsets of the first plurality of fluid passages comestogether to a single flow. Yet another example is that a globaltemperature of the first fluid refers to the temperature at a positionwhere the first fluid is flowing as a single flow.

As illustrated in FIG. 4, the plate heat exchanger 1 includes a platepackage P, which is formed by a number of heat exchanger plates A, B,which are provided side by side. In the disclosed embodiments, the heatexchanger plates include two different plates, which in the followingare referred to as a first heat exchanger plate A and a second heatexchanger plate B.

The heat exchanger plates A, B are provided side by side in such amanner that a first fluid passage 3 is formed between each pair ofadjacent first heat exchanger plates A and second heat exchanger platesB, and a second fluid passage 4 is formed between each pair of adjacentsecond heat exchanger plates B and first heat exchanger plates A. Thus,the heat exchanger comprises a first plurality of fluid passages 3 and asecond plurality of fluid passages 4.

Each fluid passage has a local inlet 41 and a local outlet 42. Eachlocal inlet and local outlet may in turn comprise a plurality ofentrances to or exits from the space between a pair of adjacent heatexchanger plates forming the fluid passage. Thus, by local inlet to afluid passage is meant one or more entrances to the fluid passage, andby local outlet from a fluid passage is meant one or more exits from thefluid passages.

The plate package P further includes an upper end plate 6 and a lowerend plate 7 provided on a respective side of the plate package P.

As appears from especially FIGS. 3 and 4, substantially each heatexchanger plate A, B has four portholes 8.

The first of the portholes 8 forms a first inlet channel 9 to the firstplurality of fluid passages, including first fluid passage 3, whichextends through substantially the whole plate package P, i.e. all platesA, B and the upper end plate 6. The second of the portholes 8 forms afirst outlet channel 10 from the first plurality of fluid passages,which also extends through substantially the whole plate package P, i.e.all plates A, B and the upper end plate 6.

The third of the portholes 8 forms a second inlet channel 11 to thesecond plurality of fluid passages, including the second fluid passage4. The fourth of the portholes 8 forms a second outlet channel 12 fromthe second plurality of fluid passages. Also these two channels 11 and12 extend through substantially the whole plate package P, i.e. allplates A, B and the upper end plate 6.

Now turning to FIG. 5, a first embodiment of the inventive system willbe discussed. The system comprises an evaporator 54 in the form of aplate heat exchanger. The evaporator 54 comprises heat exchanger platesA, B configured as discloses above in connection to FIGS. 2-4. Thus, theevaporator 54 comprises a first plurality of fluid passages 3 and asecond plurality of fluid passages 4.

In FIG. 5, the first plurality of fluid passages are represented by thefirst fluid passages denoted 3 a and 3 b. Each first fluid passage 3 a,3 b has a local inlet and a local outlet. The evaporator 54 has a globalinlet and a global outlet 13. The fluid passages 3 a, 3 b are arrangedsuch that a first fluid may be supplied through the evaporator 54 fromthe global inlet to the global outlet 13 via the fluid passages 3 a, 3b.

The global outlet 13 of the evaporator 54 is connected to an inlet 14 ofa compressor 51 via a tube system 15. An outlet 16 of the compressor 51is via another tube system 17 connected to an inlet 18 of a condenser52. An outlet 19 of the condenser 52 is connected to a plurality ofinjector arrangements 25 a, 25 b. In the disclosed embodiment, eachinjector arrangement 25 a, 25 b comprises a valve 22 a, 22 b and anozzle 27 a, 27 b.

It is to be understood that in its easiest form, an injector arrangementmay be constituted by a valve providing a fluid distribution. Theinjector arrangements 25 a, 25 b are connected to one or more localinlets of a first fluid passage 3 a, 3 b in the first plurality of fluidpassages of the evaporator 54. Thus, a closed circulation system isprovided.

Each injector arrangement 25 a, 25 b in the plurality of injectorarrangements, see FIG. 6, is arranged to supply a flow of a first fluidto a local inlets of a first fluid passage 3 a, 3 b for evaporation ofthe first fluid before leaving the evaporator 54 via its global outlet13. Alternatively, one or more of the injector arrangements may bearranged to supply a flow of a first fluid to the local inlets of morethan one of the first fluid passages in the first plurality of fluidpassages.

No matter how the injectors arrangements 25 a, 25 b are arranged, it ispreferred that the flow is directed essentially in a direction inparallel with the flow direction through the first plurality of fluidpassages 3. Thereby any undue re-direction of the fluid flow may beavoided. In case of the heat exchanger being a plate heat exchanger thismeans in parallel with the general plane of the first and the secondheat exchanger plates.

In the disclosed embodiment, the valves 22 a, 22 b of the injectorarrangements 25 a, 25 b are positioned exterior of the evaporator 54 andof the plate package P making up the same, whereas the nozzles 27 a, 27b of the injector arrangements 25 a, 25 b are arranged to extend to theinterior of the evaporator 54 via evaporator inlets 26 a, 26 b, in awall portion of the plate package.

The evaporator inlets 26 a, 26 b are in the form of through holes havingan extension from the exterior of the plate package P to the interior ofthe plate package and more precisely to the local inlets of the firstplurality of fluid passages. The through holes may be formed by plasticreshaping, by cutting or by drilling. The term plastic reshaping refersto a non-cutting plastic reshaping method such as thermal drilling. Thecutting or drilling may be made by a cutting tool. It may also be madeby laser or plasma cutting.

As an alternative embodiment, as mentioned above, each injectorarrangement 25 a, 25 b may comprise only a valve which both controls theflow and functions as a nozzle. Thus, in its most simple form thenozzles 27 a, 27 b may be omitted whereby the flow of fluid may beprovided from a through hole (not disclosed) or a pipe (not disclosed).

A cross-section of the inlet area of an evaporator possible to be usedin the inventive system is disclosed in FIG. 6. The inlet channel 9 ofthe embodiment of FIG. 4 has been replaced by each first fluid passage,in the first plurality of fluid passages 3, receiving an injectorarrangement 25 a, 25 b.

It is to be understood that each injector arrangement 25 a, 25 b maycomprise a plurality of nozzles, wherein the plurality of nozzles areprovided with fluid from a single valve. It is also to be understoodthat each injector arrangement 25 a, 25 b may comprise a plurality ofvalves.

It is to be understood that the number of injectors arrangements 25 a,25 b may be lower than the number of first fluid passages 3. Therebyeach injector arrangement may be arranged to supply its flow of thefirst fluid to more than one of the local inlets of the first fluidpassages 3. This may be made possible by each injector arrangement 25 a,25 b being arranged in a through hole having a diameter extending acrosstwo or more first fluid passages, whereby one and the same injectorarrangement 25 a, 25 b may supply fluid to more than one fluid passagein the first plurality of fluid passages 3.

Returning to FIG. 5, the inventive system further comprises a localsensor arrangement 29 comprising local temperature sensors. In thisfigure, the local temperature sensors are represented by the localtemperature sensors denoted 31 a and 31 b.

The local temperature sensors 31 a, 31 b are arranged to measuretemperature values corresponding to the local temperature of theevaporated first fluid flowing nearby the local outlets of the firstplurality of fluid passages 3. By the term nearby is meant around thelocal outlet, i.e. it could be either upstream or downstream from thelocal outlet in view of the first fluid. The local temperature sensors31 a, 31 b should be positioned such that they measure on flows of firstfluid after the flows have evaporated and before the flows mix with eachother to form a global flow.

The local temperature sensors 31 a, 31 b may be arranged in throughholes having an extension from the exterior of the plate package P tothe interior of the plate. Alternatively, the local temperature sensors31 a, 31 b may be arranged only interior or only exterior of the plate.The local temperature sensors 31 a, 31 b may be arranged separated fromeach other or in connection to each other by for example attachment to aflute shaped device extending along an outlet channel common for thelocal outlets of the first plurality of fluid passages 3.

It is to be understood that by measuring temperature valuescorresponding to the local temperature of the evaporated fluid is meantthat the measurement does not need to be performed directly on or indirect connection to the first fluid flowing nearby the local outlets.Different embodiments of how the temperature may be measured will bedisclosed in connection to FIGS. 7-9 to be discussed below.

The local temperature sensors 31 a, 31 b may be arranged to measuretemperatures in connection to one or more fluid passages 3 a, 3 b.Alternatively, the local sensor sensors 31 a, 31 b may be arranged tomeasure an average temperature value.

The local sensor arrangement 29 does not need to be arranged to measurethe temperature corresponding to the local temperature of the firstfluid in all in the first plurality of fluid passages 3. For example,the local temperature sensors 31 a, 31 b may be arranged such that thetemperatures corresponding to the local temperatures of the first fluidflowing nearby the local outlets of every tenth pair of fluid passagesin the first plurality of fluid passages 3 are measured.

The local temperature sensors 31 a, 31 b are connected to a controller57. The controller 57 is arranged to communicate with the local sensorarrangement 29 and with the individual valves 22 a, 22 b of the injectorarrangements 25 a, 25 b. The controller 57 may be for example a Pregulator, a PI regulator or a PID regulator.

By the local sensor arrangement 29, the temperatures at local positionswithin the heat exchanger may be determined. The purpose of the localsensor arrangement 29 is to determine the local temperatures in ornearby the local outlets of one or several first fluid passages 3 a, 3 bin order to enabling determining and executing a local adjustment of theflow of first fluid in the first plurality of fluid passages 3.

The controller 57 is arranged to receive the measured local temperaturevalues from the local sensor arrangement 29. The controller 57determines a difference between the measured temperature values. One ormore differences may be determined based on a single batch of measuredtemperature values.

Based on the determined difference, the controller 57 determines a localadjustment of the local amount of first fluid supplied by at least oneof the injector arrangements 25 a, 25 b. The controller 57 may determineone or more local adjustments based on a single batch of measuredtemperature values received from the local sensor arrangement 29.Different injector arrangements 25 a, 25 b may be adjusted to adifferent degree.

The difference may be determined by determining the standard deviationof the measured temperature values received from the local sensorarrangement 29. By utilizing the standard deviation for determining thelocal adjustment, quick and harsh local adjustments are damped such thatthe adjustment procedure becomes more smooth and even.

It is to be understood that the controller 57 does not need to base theadjustment on all of the received measured temperature values. Forexample, the controller 57 may determine an adjustment in flow in viewof a particular injector arrangement based on a selected number ofmeasured temperature values, such as those corresponding to the adjacentinjector arrangements, or of a mean value of a number of measuredtemperature values.

The local adjustment is performed in order to even out any temperaturedifferences in view of the first fluid flowing nearby the local outlets.The overall ambition with the local adjustment may thus be seen as theambition that all first fluid passages 3 should contribute equally tothe overall operation of the evaporator.

For example, in known heat exchangers, the global amount of flow isadjusted if liquid content is detected in the global outlet ordownstream from the global outlet 13. However, the presence of liquidcontent in the global flow may be caused by a local overflow in a singlefluid passage or in a subset of fluid passages. By measuring localtemperatures and evening out the differences between the temperatures inthe first fluid flowing nearby the local outlets, only the local flow inthe specific fluid passage or passages causing the liquid content isadjusted.

The presence of any liquid content in a local flow may be detected bymeans of the local sensor arrangement 29 if the local sensors 31 a, 31 bare arranged to measure directly on the first fluid nearby the localoutlets of the first plurality of fluid passages 3. If any liquidcontent is present nearby a local temperature sensor 31 a, 31 b, theliquid substance will attach to the sensor and evaporate there from. Dueto the evaporation, the affected local temperature sensor 31 a, 31 bwill measure a temperature value being lower than temperature valuesfrom local temperature sensors which measure on a fully evaporated firstfluid.

By the inventive system and method, the amount of first fluid in thefirst fluid passage or passages in which the measured local temperaturevalues are low is adjusted such that all fluid supplied thereto maybecome evaporated and thus the measured temperature values shouldincrease towards the measured local temperature value of other firstfluid passages.

Thus, by the inventive system and method, the first plurality of fluidpassages 3 may be utilized more efficiently as compared to knowntechniques. Further, by optimizing the flow in the plurality of firstfluid passages 3, a higher pressure may be achieved in the global flowdownstream from the global outlet. In systems such as the oneillustrated in FIG. 5, the efficiency of the compressor 51 is increasedwhen fed with a higher pressure. Thus, the efficiency of the wholesystem may be boosted.

The system further comprises a global sensor arrangement 28. In thedisclosed embodiment, the global sensor arrangement 28 comprises aglobal pressure sensor 30 a and a global temperature sensor 30 b. Theglobal sensor arrangement 28 may be arranged in the tube system 15connecting the global outlet 13 of the evaporator 54 with the inlet 14of the compressor 51 and more precisely in or downstream from the globaloutlet 13 of the evaporator but before the inlet 14 of the compressor51.

The two global sensors 30 a, 30 b must not have the same position withinthe system. However, it is preferred that the global sensor arrangement28 is arranged at essentially the same position, such that the globalsensors 30 a, 30 b measures on the same portion of evaporated firstfluid.

It may also be possible to arrange the global sensor arrangement 28 or apart thereof in the outlet channel (not disclosed) of the evaporator 54.

The global pressure sensor 30 a is preferably arranged after the globaloutlet 13 of the evaporator 54 in a more or less straight section of thetube system 15 connecting the evaporator 54 with the compressor 51.Depending on the configuration of the tube system 15 it may, as a ruleof thumb, be preferred, that the global pressure sensor 30 a is arrangedon a distance after a tube bend corresponding to at least ten times theinner diameter of the tube, and on a distance before a tube bendcorresponding to more than five times the inner diameter of the tube. Insome embodiments it is preferred that the global sensor arrangement 28is arranged nearby the inlet 14 of the compressor 51.

The global pressure sensor 30 a is arranged to measure the globalpressure value of the evaporated first fluid, in the followingidentified as the measured global pressure.

The global pressure sensor 30 a may for example be a 4-20 mA pressuresensor with a range from 0 to 25 bars.

The global temperature sensor 30 b is preferably arranged in the tubesystem 15 after a tube bend. It is preferred that the temperature sensor30 b is arranged closer to the inlet 14 of the compressor 51 than to theglobal outlet 13 of the evaporator 54. By positioning the temperaturesensor 30 b after a tube bend it is more likely that any remainingliquid content in the evaporated first fluid is evaporated while meetingthe walls of the tube bend and thereby being forced to change its flowdirection. There is also an evaporation taking place by the remainingliquid contents absorbing heat from the surrounding superheated fluidflow.

The global temperature sensor 30 b may be a standard temperature sensormeasuring the temperature, in the flowing identified as the measuredtemperature.

The measured values regarding global pressure and global temperature arecommunicated to the controller 57 which is arranged to regulate thesystem on a global level based on the determined superheating.Alternatively, or in addition, the controller 57 may base the regulationon a detection of presence of liquid content which may be performed byat least one temperature sensor included in the global sensorarrangement 28.

The superheating, being a physical parameter well known in the art, isdefined as the temperature difference between the present temperatureand the saturation temperature at a prevailing pressure, i.e. when thereis not any liquid content remaining in the fluid. The superheating isunique for a given fluid and for a given temperature and pressure. Thesuperheating may be found in conventional graphs or tables.

Generally, the closer the measured temperature comes to the saturationtemperature, the more efficient the system becomes. That is, the amountof fluid supplied to the heat exchanger is completely evaporated and notunnecessary overheated.

However, the closer the measured temperature comes to the saturationtemperature, the closer it comes to flooding the system withnon-evaporated fluid, i.e. the evaporator is incapable of evaporatingthe supplied amount of fluid. Solely for illustrative purpose, thesuperheating may be regarded as being digital—either there is a completeevaporation without any liquid content, or there is an incompleteevaporation with liquid content contained in the evaporated flowdownstream the evaporator.

In order to optimize the operation of an evaporator it is desired tohave as low superheating as possible. However, since a compressor issensitive to liquid content and may be damaged thereby, its commonpraxis to use a safety margin of some degrees when designing anevaporation system. Typically, a normal safety margin for a prior artevaporator is 5° K, i.e. the superheating should be at least 5° K.However, it is to be understood that another value of the safety marginmay be elected.

In its most simple form, the safety margin is to be regarded as aconstant decided by the intended use of the evaporator. It is however tobe understood that there is also a desire to use as low safety margin aspossible since there is an economical interest of operating theevaporator as close to the saturation temperature as possible. Duringthe operation of the system this constant will be used as a set-pointsuperheating, i.e. a target value, towards which the operation of theevaporator 54 will be dynamically controlled.

The global amount of first fluid in the first plurality of fluidpassages 3 are thus adjusted in order to reach the set-pointsuperheating, or in order to remove the presence of any liquid content.The global tuning works as an optional complement to the local tuning ofthe local flows within the heat exchanger which is controlled based onvalues measured by the local sensor arrangement 28.

The purpose of the global sensor arrangement 28 is thus to determine thepresence of any liquid content in the evaporated first fluid, or todetermine the so called superheating of the evaporated first fluid. Themeasurements are transmitted to the controller 57 which, in turn,determines a global adjustment of the flow of first fluid in the firstplurality of fluid passages 3.

Thus, in one embodiment, the local flow in a subset of the firstplurality of fluid passages 3 is controlled by measuring localtemperature values by the local sensor arrangement 29, and the globalflow in the first plurality of fluid passages 3 is controlled bymeasuring global temperature and/or pressure values by the global sensorarrangement 28.

The global adjustment may be described as an adjustment in order tooperate towards a set-point superheating or towards the non-presence ofliquid content, whereas the local adjustment may be described as anadjustment for evening out the temperature differences within the heatexchanger. Both adjustments are performed in order to optimize theperformance of the heat exchanger. The adjustments complement each otherbut may also function on their own. For example, a system may comprisethe local sensor arrangement 29 and perform the local tuning of thefirst plurality of fluid passages 3 without utilizing the global sensorarrangement and global adjustment.

The local adjustment and optionally the global adjustment are preferablyperformed continuously for the system during operation thereof. Thus,the local flow and optionally also the global flow are adjustedcontinuously whereby the heat exchanger is continuously optimized inview of current running conditions and operation duty. The heatexchanger thus becomes more flexible and adapts to different runningconditions. The heat exchanger will run in an optimized mannerregardless of the running conditions.

The two processes may be performed as parallel loops in the controller57.

The positioning of the local sensor arrangement will now be disclosedwith reference to FIGS. 7-9. In these figures, both the first pluralityof fluid passages and the second plurality of fluid passages areillustrated highly schematically.

As mentioned earlier, the local sensor arrangement is arranged tomeasure temperature values corresponding to the local temperatures ofthe evaporated first fluid flowing nearby the local outlets of the firstplurality of fluid passages. Thus, the sensors 31 a, 31 b of the localsensor arrangement 29 may measure directly or indirectly on theevaporated first fluid flowing nearby the local outlets.

Referring generally to the FIGS. 7-9, a first fluid is supplied to afirst plurality of fluid passages by injector arrangements 25 a, 25 b.The flow of first fluid through the first plurality of fluid passages isindicated by 74. A second fluid is supplied to a second plurality offluid passages. The flow of second fluid through the second plurality offluid passages is indicated by 75. The second fluid enters the heatexchanger via a global inlet 71 and exits the heat exchanger via aglobal outlet 72. When flowing through the respective fluid passages,heat is transferred between the first fluid and the second fluid.

Different embodiment of how the local sensors 31 a, 31 b may be arrangedwill now be disclosed.

As a first example, the local temperature sensors 31 a, 31 b are in FIG.7 arranged nearby the local outlets of the first plurality of fluidpassages, and the local temperature sensors 31 a, 31 b are arrangedwithin the housing of the heat exchanger. In this embodiment, the localoutlets of the first plurality of fluid passages exits in a commonoutlet channel ending in a global outlet 76 from the heat exchanger. Theglobal outlet 76 corresponds to the first outlet channel 10 of FIG. 3.The local temperature sensors 31 a, 31 b is in this embodimentattachment to a flute shaped device 73 extending along common outletchannel.

As a second example, the local temperature sensors 31 a, 31 b are inFIG. 8 arranged also nearby the local outlets of the first plurality offluid passages, but instead in a position exterior of the plate packageP and outside the housing of the heat exchanger. The local temperaturesensors 31 a, 31 b are arranged in so called ports 80 a, 80 b locatedbetween the housing and a common outlet.

As a third example, the local temperature sensors 31 a, 31 b are in FIG.9 arranged nearby the local outlets of the second plurality of fluidpassages. Thus, the local sensors are in this embodiment not arranged indirect or even indirect connection to the first fluid. However, it hasbeen realized by the inventors that there exists a relation between thelocal temperature of the second fluid flowing nearby the local outletsof the second plurality of fluid passages and the local temperature ofthe first fluid flossing nearby the local outlets of the first pluralityof fluid passages. More precisely, the local temperature of the secondplurality of fluid passages reflects the local temperature of the firstfluid. The measured temperature values at the second plurality of fluidpassages may therefore in this embodiment be utilized in the controllerfor determining local adjustments in order to even out differencesbetween the measured temperature values.

By measuring on the second fluid, the measurement procedure may besimplified. Firstly, the second plurality of fluid passage may provide afriendlier environment for the sensors in case the second fluid iswater. Secondly, it may be easier to arrange temperature sensors in thesecond plurality of fluid passages without affecting the fluid. Thirdly,the measured temperature values on the second fluid may be utilized forfurther purposes, such as providing information regarding the outgoingsecond fluid temperature to a user.

The measurement on the second fluid may be performed inside the heatexchanger or outside of the heat exchanger in analogy with thearrangement of the local sensors 31 a, 31 b when arranged to measure onthe first fluid (i.e. FIGS. 7 and 8).

It is to be understood that the local sensor arrangement may be arrangedto measure directly on the fluid or indirectly, such as by measuring onheat-conducting pipes in which the fluid flows.

A method according to one embodiment of the present invention forperforming the local adjustment of the heat exchanger, based on themeasurement of the local sensor arrangement, will now be disclosed withreference to FIG. 10. The heat exchanger system as such has the samegeneral design as that previously described with reference to FIG. 5whereby reference is made thereto.

As a first step, a first fluid and a second fluid is supplied 1001. Thefirst fluid is supplied by the plurality of injector arrangements to thefirst plurality of fluid passages 3. The second fluid is supplied to thesecond plurality of fluid passages 4.

As a following step, temperature values corresponding to localtemperatures of the evaporated first fluid flowing nearby the localoutlets of the first plurality of fluid passages 3 are measured 1002.

As a following step, the measured temperature values are transmitted1003 to the controller 57.

As a following step, a difference between the measured temperaturevalues is determined 1004. The difference may for example be determinedby determining the standard deviation for the measured temperaturevalues.

As a following step, a local adjustment is determined 1005. The localadjustment is an adjustment of the local amount of fluid supplied by atleast one of the plurality of injector arrangements, in order to evenout the determined difference. One or more local adjustments may bedetermined based on the same batch of measured temperature values. Forexample, a first local adjustment to be applied to a first injectorarrangement may be determined together with a second local adjustment tobe applied to a second injector arrangement and to a third injectorarrangement.

The method may further comprise a step of determining a compensatinglocal adjustment of the local amount of first fluid supplied by theother injector arrangements for which no local adjustment has beendetermined. As a continuation of the example above, a compensating localadjustment may be determined for a fourth injector arrangement. Thecompensating local adjustment is determined in order to keep the globalamount of first fluid in the plurality of first passages unaffected bythe local adjustments. The global amount is instead controlled based onthe values measured by the global sensor arrangement.

As a following step, the local adjustment is communicated 1006 from thecontroller 57 to the valves of the affected injector arrangement. Thus,the local amount of first fluid supplied by that specific injectorarrangement is adjusted according to the determined local adjustment.

The compensating local adjustment, if any, is also communicated to thevalves of the affected injector arrangements.

The method may be performed continuously in the heat exchanger. Themethod may further be performed in parallel with global adjustment ofthe global amount of flow of first fluid.

A global adjustment method will in the following be disclosed withreference to FIG. 11. The system as such has the same general design asthat previously described with reference to FIG. 5 whereby reference ismade thereto.

The global sensor arrangement 28 downstream the global outlet 13 of theheat exchanger measures 1101 the presence of any liquid content in theglobal flow of first fluid or measured global pressure Pm and globaltemperature Tm. The signal generated by the global sensor arrangement 28is received 1102 by the controller 57. The controller may be a Pregulator, a PI regulator or a PID regulator.

The controller 57 evaluates 1103 the received signal.

When measuring the presence of any liquid content, the signal may in itsmost simple form be a digital signal: 1—no liquid content detected;0—liquid content detected. More precisely, a signal having the value 1indicates that the evaporated fluid has a measured temperaturecorresponding to or being above the superheating. Likewise, a signalhaving the value 0 indicates that the evaporated fluid has a temperaturebeing below the superheating.

Alternatively, the superheating may be determined by firstly convertingthe measured global pressure value to a saturation temperature andsecondly establish the superheating by comparing the measured globaltemperature value with the determined saturation temperature.

As a following step, the controller 57 determines 1104 a suitable globaladjustment of first fluid supplied by the plurality of injectorarrangement, based on the determined liquid content or determinedsuperheating.

As a following step, the controller 57 communicates with the valves ofthe injector arrangements, or with a global valve, to adjust the globalflow according to the determined global adjustment. The global valve maybe a main valve arranged upstream from the injector arrangements, whichvalve controls the total supply of first fluid to all injectorarrangements.

The invention has been described as applied to a heat exchanger being aplate heat exchanger. However, it is to be understood that the inventionis applicable no matter form of evaporator or heat exchanger.

The injector arrangements are disclosed as being arranged in throughholes extending from the exterior of the plate package into theindividual fluid passages. It is to be understood that this is only onepossible embodiment. For example, the injector arrangements may extendinto any inlet port or the like depending on the design of theevaporator. This may for example be made by a flute device arrangedalong an inlet channel.

The invention has generally been described based on a plate heatexchanger having first and second plate passages and four port holesallowing a flow of two fluids. It is to be understood that the inventionis applicable also for plate heat exchangers having differentconfigurations in terms of the number of plate passages, the number ofport holes and the number of fluids to be handled.

It is to be understood that the controller may be used for otherpurposes as well, such as control of the refrigerant circuit as such.

The invention is not limited to the embodiment disclosed but may bevaried and modified within the scope of the following claims, whichpartly has been described above.

1. A system for dynamic control of the operation of a heat exchanger,the system comprising a heat exchanger, a plurality of injectorarrangements, a local sensor arrangement, and a controller, wherein theheat exchanger comprises a first global outlet, a first plurality offluid passages, each fluid passage comprising a local inlet and a localoutlet, for the supply of a first fluid to the first global outlet viathe first plurality of fluid passages during evaporation of the firstfluid; the heat exchanger further comprises a second global outlet, asecond plurality of fluid passages, each fluid passage comprising alocal inlet and a local outlet, for the supply of a second fluid to thesecond global outlet via the second plurality of fluid passages; thefirst fluid passages and the second fluid passages are arrangedseparated from each other and side-by-side, in order to enable heatexchange between the first fluid in the first plurality of fluidpassages and the second fluid in the second plurality of fluid passages;each injector arrangement comprises at least one valve, and eachinjector arrangement is arranged to supply a flow of the first fluid tothe local inlet of at least one of the first plurality of fluidpassages; the local sensor arrangement comprises a plurality of localtemperature sensors being arranged to measure temperature valuescorresponding to the local temperature of the evaporated first fluidflowing nearby the local outlets of the first plurality of fluidpassages; the controller is arranged to determine a difference betweenthe measured temperature values received from the local sensorarrangement and is further arranged to communicate with the valves ofthe plurality of injector arrangements to adjust the local amount offirst fluid supplied by at least one of the injector arrangements inorder to even out the determined difference.
 2. The system according toclaim 1, wherein the plurality of local temperature sensors in the localsensor arrangement are arranged nearby the local outlets of the firstplurality of fluid passages.
 3. The system according to claim 1, whereinthe plurality of local temperature sensors in the local sensorarrangement are arranged nearby the local outlets of the secondplurality of fluid passages.
 4. The system according to claim 1, whereinthe controller is further arranged to determine a compensating localadjustment of the local amount of first fluid supplied by the other thanthe at least one of the injector arrangements such that the globalamount of first fluid in the first plurality of first passages remainsthe same, and communicate the determined compensating local adjustmentto said other than the at least one of the injector arrangements.
 5. Thesystem according to claim 1, wherein the controller is arranged todetermine the difference by at least determining the standard deviationfor the measured temperature values.
 6. The system according to claim 1,wherein the first fluid is refrigerant and the second fluid compriseswater.
 7. The system according to claim 1, wherein the controller is aPI regulator or a PID regulator.
 8. The system according to claim 1,wherein the system further comprises a global sensor arrangement beingarranged to measure the global temperature and the global pressure, orthe presence of any liquid content, of the evaporated first fluiddownstream from the first global outlet; the controller is arranged tocommunicate with the valves of the plurality of injector arrangements,or with a global valve, to control, based on information received fromthe global sensor arrangement, the global amount of the first fluid tobe supplied to the first plurality of fluid passages in order for theheat exchanger to operate towards a set-point superheating value.
 9. Thesystem according to claim 8, wherein the global sensor arrangementcomprises a global pressure sensor and a global temperature sensor. 10.Use of a system according to claim
 1. 11. A method for dynamic controlof the operation of a heat exchanger in a system according to claim 1,the method comprising: a) supplying, by the plurality of injectorarrangements, a first fluid to the local inlets of the first pluralityof fluid passages, and supplying a second fluid to the local inlets ofthe second plurality of fluid passages; b) measuring, by the localsensor arrangement, temperature values corresponding to the localtemperatures of the evaporated fluid flowing nearby the local outlets ofthe first plurality of fluid passages; c) transmitting the measuredtemperature values to the controller; d) determining, by the controller,a difference between the measured temperature values; e) determining, bythe controller, a local adjustment of the local amount of fluid suppliedby at least one of the plurality of injector arrangements based on thedetermined difference, in order to even out the determined difference,f) communicating, by the controller, with the valves of the plurality ofinjector arrangements to adjust the local amount of first fluid suppliedby at least one of the plurality of injector arrangements according tothe determined local adjustment.
 12. The method according to claim 11,further comprising: determining a compensating local adjustment of thelocal amount of first fluid supplied by the other than the at least oneof the injector arrangements in order to keep the global amount of firstfluid in the plurality of first passages unaffected by the localadjustments; and communicating, by the controller, with the valves ofthe plurality of injector arrangements to adjust the local amount offirst fluid supplied by said other than the at least one of theplurality of injector arrangements according to the determinedcompensating local adjustment.
 13. The method according to claim 11,wherein the determining of the difference comprises determining thestandard deviation for the measured temperature values.
 14. The methodaccording to claim 11, wherein the system further comprises a globalsensor arrangement comprising a global temperature sensor and a globalpressure sensor, the method further comprising: g) measuring, by theglobal sensor arrangement, a global temperature value and a globalpressure value of the evaporated first fluid downstream from the firstglobal outlet; h) transmitting the measured global temperature value andmeasured global pressure value to the controller; i) determining, by thecontroller, the superheating value based on the measured globaltemperature value and the measured global pressure value; j)determining, by the controller, the difference between the determinedsuperheating value and a set-point superheating value, or the presenceof any liquid content in the evaporated first fluid; k) determining, bythe controller, a global adjustment of the amount of first fluidsupplied by the plurality of injector arrangements, required to reachthe set-point superheating value, l) communicating, by the controller,with the valves of the plurality of injector arrangements, or with aglobal valve, to adjust the global amount of first fluid supplied by theplurality of injector arrangements according to the determined globaladjustment.
 15. The method according to claim 14, wherein the stepsb)-f) and the steps g)-l) are performed in parallel.
 16. The methodaccording to claim 14, wherein the steps b)-f) and the steps g)-l) arecontinuously performed as parallel loops in the controller.